The present invention relates generally to solenoid valves and more particularly to a pulse width modulated solenoid valve for variable displacement control and which is suitable for use in electronically controlled air conditioning compressors.
Control of displacement in automotive air conditioning compressors has conventionally been accomplished using a mechanical control. In order to replace the mechanical control with an efficient electronic control it would be desirable to utilize a pulse width modulated solenoid valve. However, the input pressure of the Freon oil mixture is typically between 30 and 350 psi and presently available solenoid valves capable of operating at these pressure ranges under automotive environmental conditions are quite expensive. To be practical for use in mass produced vehicles, the solenoid valve must be manufacturable to very close tolerances and yet must be economical. Currently available valves are generally deficient in this regard.
The present invention provides an economical valve which is well suited to the automotive air conditioning compressor control application. It employs a unique construction in which the critical air gap tolerances are readily adjusted during manufacture with a minimal number of manufacturing steps and using a minimal number of parts. Unlike conventional valves in which a large number of components are stacked together, each contributing to tolerance variations, the present valve is constructed so that the critical gap dimension is established by a simple length adjustment of a rod and armature assembly. By this simple adjustment, the individual components which make up the valve no longer contribute to cumulative tolerance variations. Thus the valve of the invention is easy to manufacture without a great deal of high tolerance manufacturing steps.
According to one aspect of the invention the solenoid valve comprises a tubular housing which defines a longitudinal axis and which has a substantially closed end that defines a first reference plane. The first reference plane is generally orthogonal to the longitudinal axis. The tubular housing also has a substantially open end, opposite the closed end. A solenoid coil is disposed about the tubular housing for producing an electromagnetic force. An armature is slidably disposed in the tubular housing for longitudinal movement along the longitudinal axis. The armature has a first face that is adjacent the substantially closed end and a second face that faces the substantially open end.
A pole piece member, at least partially disposed on and preferably inserted into the tubular housing, covers the substantially open end. The pole piece member has a longitudinal passageway in axial alignment with the longitudinal axis. The pole piece member further has an alignment face which defines a second reference plane generally orthogonal to the longitudinal axis. A first spring is compressibly disposed between the closed end of the tubular housing and the adjacent armature face. The spring urges the armature towards the pole piece.
A longitudinal rod of a predetermined length is slidably disposed in the longitudinal passageway of the pole piece. The rod is secured to the armature by a means which permits the combined longitudinal length of the rod and the armature to be adjusted to a predetermined controlled dimension. In the presently preferred embodiment a press fit is used between the longitudinal rod and the armature.
The solenoid valve further comprises a solenoid housing for carrying the pole piece and the tubular housing so that the alignment face of the pole piece member faces longitudinally outwardly. Secured to the solenoid housing is a valve structure which has an alignment face disposed for registration with the alignment face of the solenoid housing to thereby establish a fixed spatial relationship between the valve and the pole piece and to thereby establish a fixed spacing between the first reference plane and the second reference plane. The valve may include a valve seat, a movable valve member for registration with the valve seat and a second spring for urging the valve member into contact with the valve seat.
The longitudinal rod extending from the armature has an end that is disposed in force imparting communication with the valve member. The armature is responsive to electromagnetic forces of the solenoid coil to produce longitudinal movement of the longitudinal rod. The rod thus imparts longitudinal forces to the valve member and these forces tend to compress the second spring causing the valve member to move to an unseated or open position.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.